Composite products comprising cellulosic materials and synthetic resins and methods of making the same

ABSTRACT

New wood-synthetic resin composite products and methods of forming these products are provided. The products comprise a cellulosic or fibrous material and polypropylene (preferably reactor flake polypropylene). The products are formed by passing ingredients including the fibrous material and polypropylene through an extruder (preferably a twin screw extruder) at temperatures of from about 150-260° C. The extruded composite products have physical properties very similar to those of natural wood, including high tensile strengths, high compressive strengths, and high densities.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present is concerned with new wood-synthetic resin compositeproducts and extrusion processes for forming these products.

2. Description of the Prior Art

Although wood is a naturally reproducible resource, the demand for woodis consistently high. Furthermore, the supply of good wood forconstruction purposes is beginning to diminish. Accordingly, there is anincreasing urgency to find alternative sources of wood. One possiblealternate source is through the production of artificial wood from amixture of ingredients including recycled wood scraps such as wood meal,wood chips, saw dust, and newspapers, which are each by-products ofindustrial wastes and other industries using natural wood products.

Composite materials consisting of recycled wood scraps and athermoplastic material have been known for many years. Generally, thesecomposites are formed so that they may be used in many of the sameapplications as an all-wood product while offering advantages such ashigh resistance to rot, insects, and moisture. These products can havethe same workability as wood and are splinter-free. However, thesecomposites have not been successfully used as a direct replacement forwood.

Forming a wood-polymer composite into a final product has beenaccomplished using most oft he techniques used for forming all-polymerproducts, including extrusion. While the technology for extrudingall-polymer products is well developed with fairly predictable results,the extrusion of a wood-thermoplastic composite material using recycledinput materials is subject to a much wider variance in the molecularmakeup and physical characteristics of the input materials, dependingupon available resources of the recycled material. Moreover, awood-thermoplastic composite has unique melt flow characteristics whichprevent the literal translation of polymer extrusion techniques for usein composite material extrusion.

Previous extruded wood-polymer composites have generally comprisedpolyethylene as the polymer. While extrusion processes are the preferredmethod for forming these composites due to the ease with which largequantities of the composite can be readily manufactured, it haspreviously been impossible to form wood-polypropylene composites bycounter-rotating, twin screw extrusion processes in a commerciallyfeasible manner. That is, manufacturers were unable to develop processconditions which properly processed large quantities of polypropylenewithout damaging the wood. Thus, there is a need for processes forextruding polypropylene and wood or other cellulosic materials to yieldsuitable composite products.

SUMMARY OF THE INVENTION

The present invention fills this need by broadly providingwood-synthetic resin composite products and methods of forming suchproducts by extrusion processes.

In more detail, the products are formed by introducing ingredientsincluding respective quantities of a fibrous or cellulosic material andpolypropylene into the inlet of an extruder (preferably a twin screwextruder). Preferably, the weigh blender is positioned immediately abovethe extruder, at the extruder inlet, so that the blend of ingredients isformed immediately prior to entering the extruder, thus minimizing orpreventing separation of the ingredients. This is not the case withprior art processes which convey the ingredients to, or “cram” theingredients into, the extruder inlet so as to cause separation of theingredients and yield an inferior composite product.

The screw(s) is then rotated at a rate of from about 10-50 rpm, andpreferably from about 15-34 rpm to advance the ingredients through theextruder barrel and out the extrusion die to form the composite product.Preferably, the screw(s) has a compression ratio of from about 2:1 toabout 4:1, and more preferably from about 2.8:1 to about 3.6:1.

The temperature of the ingredients in the extruder barrel is preferablyfrom about 150-260° C., and more preferably from about 175-230° C. Theretention time of the ingredients in the barrel should be from about20-120 seconds, and more preferably from about 40-80 seconds. Finally,the ingredients should be advanced through the barrel at a rate of fromabout 500-2,000 lbs/hr., and more preferably from about 1,000-1,500lbs/hr.

The fibrous material is preferably present in the ingredients at a levelof from about 20-80% by weight, more preferably from about 30-70% byweight, and even more preferably from about 50-70% by weight, based uponthe total weight of the ingredients taken as 100% by weight. Thepolypropylene is preferably present in the ingredients at a level offrom about 20-80% by weight, more preferably from about 30-70% byweight, and even more preferably from about 30-50% by weight, based uponthe total weight of the ingredients taken as 100% by weight.

Preferred fibrous materials include those selected from the groupconsisting of sawdust, newspaper, alfalfa, wheat pulp, wood scraps(e.g., ground wood, wood flour, wood flakes, wood chips, wood fibers,wood particles), wood veneers, wood laminates, cardboard, straw, cotton,rice hulls, paper, coconut shells, peanut shells, bagasse, plant fibers,bamboo fiber, palm fiber, kenaf, and mixtures thereof. Furthermore, theaverage particle size of the fibrous material should be less than about½ inch, and more preferably from about {fraction (1/16)}-¼ inch.Finally, the particles of the fibrous material should have an averageaspect ratio (i.e., the ratio of the length to the widest thickness) ofat least about 10:1, preferably at least about 20:1, and more preferablyfrom about 30:1 to about 50:1. The use of such long particles increasesthe flexural modulus of the product as compared to products with loweraspect ratios by at least about 25%, and preferably at least about 40%,thus causing the final composite product to have a stiffness comparableto natural wood.

The preferred polypropylen for use in the invention is reactor flakepolypropylene (i.e., the polymer flakes as they are produced in thereactor), preferably without any further treatment (e.g., without theaddition of chemical additives or modifiers) to the polyproylene. Thepreferred polypropylene has a melt index at 230° C. of from about 0-10g/10 min., preferably from about 0.1-4 g/10 min., and more preferablyfrom about 0.1-1 g/10 min. Furthermore, it is preferred that thepolypropylene has a bulk density of from about 20-40 lbs/ft³, and morepreferably from about 28-32 lbs/ft³. The average fiber length orparticle size oft he polypropylene flakes utilized should be from about350-1,000 μm, and preferably from about 500-700 μm.

The resulting composite product is in the form of a self-sustaining bodyand has an ASTM D-6109 flexural modulus of from about 600-1,100 psi/1000(i.e., 600,000-1,100,000 psi), and preferably from about 800-1,100psi/1000 (i.e., 800,000-1,100,000 psi). The product should have anactual density of from about 40-60 lbs/ft³, and preferably from about50-58 lbs/ft³.

A number of optional ingredients can also be added to modify or adjustthe properties of the final composite product. Examples of suchingredients include acrylic process aids (e.g., Rohm and Haas K175,Kaneka Kane-Ace PA-101), UV stabilizers (e.g., CYTEC 38535, CYTEC 3346),and coloring agents. If a process aid is utilized, it is preferablypresent in the ingredients at a level of from about 0.5-5% by weight,and more preferably from about 1-2% by weight, based upon the totalweight of the ingredients taken as 100% by weight. Unexpectedly, theseacrylic process aids are particularly useful in the present invention inspite of the fact that they are intended to be used in PVC productsrather than polypropylene products.

It will be appreciated that the inventive method allows for theformation of high-strength, high-stiffness composite products havingproperties which greatly resemble the properties of natural wood.Furthermore, the inventive composite products are much stiffer thanprior art polyethylene-cellulosic fiber products due to the fact thatpolypropylene is used. The products can be used in a wide number ofareas including door sills and jambs, fascia board, window edging,window sills, decorative architectural trim (e.g., deck or patiorailing), simulated hardwood flooring, and landscaping products (e.g.,raised bed edging, flowerbed edging, driveway edging).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE

The following example sets forth preferred methods in accordance withthe invention. It is to be understood, however, that this example isprovided by way of illustration and nothing therein should be taken as alimitation upon the overall scope of the invention.

The concentrations of ingredients used in this example and settings onthe Extrusiontek Milacron CM92HP twin screw extruder (available fromExtrusionTek Milacron) are shown in Table 1. The wood shavings were fedthrough a forced air dryer (set at a temperature of 150° C.) after whichthey were conveyed from the exit of the dryer, via an auger conveyor,directly into a weigh blender which weighed and proportioned theingredients as indicated. The weigh blender was mounted directly on thefeed throat or inlet of the extruder on a piece of square tubingsufficiently high to generate a stack of material on the feed throat ofthe extruder so as to force the material into the extruder under its ownweight and to prevent separation of the ingredients.

From the feed throat, the counter-rotating screws conveyed the materialthrough a series of zones within the extruder barrel. The preferredzones are as follows: a feed zone with high surface and intake volume tobegin melting of the resins; a precompression zone to begin the mixingof the ingredients and further melting of the resins; a compression zoneto accelerate the melting and form a seal for the last zone; and ametering zone where the high viscosity blend is forced through theoutlets of the extrusion die under pressure.

TABLE 1 Run Run Run #1 #2 #3 INGREDIENTS ¼″ Birch Shavings lbs/hr  60 60 — ¼″ Mixed Hardwood Shavings lbs/hr — —  60 Solvay HB9000Polypropylene^(a) lbs/hr  40  40  40 Rohm and Haas Paraloid K175^(b)lbs/hr  1.2  1.2 — Kaneka Kane-Ace PA-101^(c) lbs/hr — —  1.2Polyvisions Polyfoam CFA-3245^(d) lbs/hr  0.4  0.4  0.4 UVStabilizers^(e) lbs/hr  0.3  0.3  0.3 EXTRUSION INFORMATION Zone 1Temperature °F. 440 420 400 Zone 2 Temperature °F. 450 450 450 Zone 3Temperature °F. 380 380 380 Zone 4 Temperature °F. 380 380 380 Zone 5Temperature °F. 380 380 380 Screw Oil Temperature °F. 300 300 300 DIEZONES Zone 1 (Restrictor) °F. 400 400 400 Zones 2-6 ° F. 440- 440- 440- 500  500  500 Amps  90 150 200 Vacuum Vent in. Hg  26   27  28 ScrewThrust %  3  6  8 Screw Speed rpm  14  21   28 PREHEATER OR VMEDS^(f)Barrel ° F. — — 340 Screw ° F. — — 340 Screw, preheater rpm — —  40 Amps— —  4 Output Rate ft/min  3.5  5  7 Weight lbs/ft  2.2  2.2  2.2Flexural Modulus psi/1000 850 850 850 ^(a) Obtained from SolvayCorporation. ^(b) This is a process aid obtained from Rohm and HaasCorp. ^(c) This is a process aid obtained from Kaneka Corp. ^(d) This isa blowing agent obtained from Polyvisions, Inc. ^(e) The UV stabilizersutilized were CYTEC 3853S and CYTEC 3346 obtained from Cytec Corp. ^(f)VMEDS is an abbreviation for Vertical Melt Enhancement Delivery System.

I claim:
 1. An extruded, wood-synthetic resin composite product in theform of a self-sustaining body formed from a mixture comprising afibrous material and reactor flake polypropylene, wherein said compositeproduct has an ASTM D-6109 flexural modulus of from about600,000-1,100,000 psi.
 2. The composite product of claim 1, wherein saidfibrous material is selected from the group consisting of sawdust,newspaper, alfalfa, wheat pulp, wood scraps, wood veneers, woodlaminates, cardboard, straw, cotton, rice hulls, paper, coconut shells,peanut shells, bagasse, plant fibers, bamboo fiber, palm fiber, kenaf,and mixtures thereof.
 3. The composite product of claim 1, wherein saidfibrous material is present in said mixture at a level of from about20-80% by weight, based upon the total weight of the mixture taken as100% by weight.
 4. The composite product of claim 1, wherein saidpolypropylene is present in said mixture at a level of from about 20-80%by weight, based upon the total weight of the mixture taken as 100% byweight.
 5. The composite product of claim 1, wherein said polypropylenehas a melt index at 230° C. of from about 0-10 g/10 min.
 6. Thecomposite product of claim 1, wherein said polypropylene has a bulkdensity of from about 20-40 lbs/ft³.
 7. The composite product of claim1, wherein said reactor flake polypropylene has an average particle sizeof from about 350-1,000 μm.
 8. The composite product of claim 1, whereinsaid fibrous material comprises particles having an averagelength:thickness ratio of at least about 10:1.